Thin film magnetoresistive (MR) sensors or heads, which are typically formed of various layers deposited upon a substrate, have been utilized in magnetic data storage devices for several years. Physically distinct forms of magnetoresistance such as anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR) and spin tunneling magnetoresistance (TMR) are well known in the art. Magnetic read-back sensor designs have been built using these principles and other effects to produce devices capable of reading relatively high density data from magnetic media. In particular, three general types of MR read-back sensors have been developed: the anisotropic magnetoresistive (AMR) sensor, the giant magnetoresistive (GMR) sensor or GMR spin valve, and the magnetic tunnel junction (MTJ) sensor. Based on the positioning of electrical contacts and geometry of these sensors, a sensing current for detecting magnetic bits of information either passes perpendicular to surface planes of the layers of the sensor or in surface planes of the layers of the sensor. Thus, read-back sensors fall into two distinct categories: current-perpendicular-to-plane (CPP) sensors and current-in-plane (CIP) sensors.
As an ever-increasing amount of information is stored on a magnetic disc, it becomes difficult for MR sensors to separately read the stored information without also reading noise from adjacent stored information. To avoid reading noise from adjacent stored information, in general, a cross-track width of the MR sensor has to be reduced in proportion with increases in areal density. However, a sensitivity of certain CIP sensors, such as CIP GMR spin valves, is proportional to the cross-track width of the sensor. Thus, such CIP sensors may encounter certain limitations when used in very high areal density applications.
The sensitivity of CPP sensors is essentially independent of the cross-track width of the sensor. However, a junction resistance of certain CPP sensors, such as CPP TMR sensors, substantially increases when sensor cross-track width is reduced. This can cause impedance matching problems between the CPP TMR sensor and a preamplifier, which is electrically coupled to the sensor and electrically processes signals from the sensor. CPP GMR sensors, in general, have a very low resistance and therefore may encounter certain limitations.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.